Generally speaking, ink ducts for printing presses are widely used and many conventional forms of such ducts are disclosed in the prior art.
In offset printing, the efficiency of production is very dependent on the uniformity of ink metering. Usually, in order to adjust the inking system after pouring in the ink, the side plates of the ink duct are first resiliently brought into engagement with the duct or roller and the ink metering means, consisting of the duct or blade or the ink metering elements, are roughly adjusted with the press rollers stationary (i.e., not rotating).
It is known from practice that the ink feed from the inking system is closely dependent on temperature. Undesired local heating of the ink duct, the metering elements and the ductor roller result in stresses leading to non-uniformity of the ink on the ductor roller, which is difficult for the printer to counteract. These fluctuations in ink metering occur particularly during short breaks in the operation of the press, such as during intervals for washing, stopping or other interruptions in production printing.
In order to solve the problems of temperature fluctuations, it is already known for the inking system (see DE Patent Abstract F 10648, Appl. date: 23.6.51) or the ink duct (see DE Utility Model 1 675 538) or parts of the ink duct (DE-OS 3 325 005) or the ink metering device (DE Utility Model 1 891 449) to be heated or cooled to a predetermined operating temperature in a controlled manner with the press stationary or in operation, in order to reduce the total temperature gradient in the individual components. The resulting heating, depending on the point of application of the heat, also produces limited cancelling-out of thermal expansion, so that the thermal stresses in the ink duct, the metering means and the ductor roller may be minimized to a significant degree. The reduction in stress through thermal expansion results in a reduction in the non-uniformity of the ink on the ductor roller, which is therefore easier to control by the printer.
A disadvantage of the known methods as disclosed above, however, is that an additional adjustable-temperature heat source always has to be installed, which increases the expense and may also be difficult to physically accommodate at the required point of heat application.